The subject of the present invention is a method for cracking off glass articles, particularly drinking glasses, vases, etc., that is to say any article of glassware or crystal glassware, by means of a laser ray.
A crack-off method using a laser ray to heat up the region of the glass to be cracked off, possibly followed by mechanical contact with a cold piece in order to create a crack, is known.
This crack-off method allows thin cylindrical glass articles to be cracked off. This method is not suitable for cracking off reentrant, flared, thick or lead-rich glass articles in the light of the number of incorrectly cracked-off, cracked or broken glasses.
The crack-off operation is an important operation in glass making and in crystal glass making since correct crack-off allows the time necessary for flatting the glass to be reduced to a minimum or even, in some cases, avoids having to do any flatting. The flatting operation is described in document BE 670,504.
The subject of the present invention is a method for cracking off glassware, making it possible to correctly crack off flared glass articles, reentrant glass articles, glass articles having thicknesses ranging from 2 to 5 mm, or even higher, and articles made of lead-rich glass. For certain glass articles, particularly for articles of simple shape (for example cylindrical or approximately cylindrical shape) and for glass articles having a thickness of less than 2 mm, the method according to the invention makes it possible to obtain a cracked-off rim capable of being treated directly in a fire-finishing station, that is to say a rim not having to be flatted.
It should also be pointed out that, for articles that have to undergo a flatting operation, the method according to the invention allows easier and more rapid flatting.
DE-4,411,037 describes a method for cracking off glass hollowware, comprising a phase during which a continuous region comprising the desired line of cutting is heated by means of at least one continuous beam of laser rays and one phase during which this region thus heated is cooled. Before or after the heating phase, a short initiating notch is formed, on the desired line of cutting, either by means of a punch or by means of a focused beam of laser rays.
The method according to the invention is a crack-off method for glassware, in which the articles of glassware rotating about an axis are subjected to a treatment by means of a laser ray. It is characterized in that,
in a first step, a rotating article to be cracked off is subjected to a continuous beam of laser rays or to continuous beams of laser rays,
so as to define, on the article to be cracked off, a continuous region touched by the said continuous laser beam or beams, and
so that the said beam or beams touch one or more parts of the said region with a power density per unit area of less than 30 W/mm2, advantageously less than 25 W/mm2, particularly from 5 to 20 W/mm2, and in that,
in a second step, during substantially one rotation of the article to be cracked off or during at least one rotation of the article to be cracked off, the region that was subjected in the first step to the action of one or more continuous beams of laser rays is subjected to the action of a focused pulsed laser beam having a power of less than 250 W so as to form a series of successive points separated from each other, the said series defining an approximately continuous line in the said part, the crack-off taking place substantially along the said line.
The term xe2x80x9cfocused pulsed laserxe2x80x9d should be understood to mean a laser intermittently emitting a laser beam or a laser ray or emitting a laser beam or a laser ray whose power varies over time between a low power, for example a minimum (particularly zero) power and a high power, for example a maximum power, in order to form, on the rotating glass article, a series of points of impact by means of the high-power beam or ray, two successive points of impact being separated from each other. The expression xe2x80x9chigh power of the beam or rayxe2x80x9d means a power sufficient to form microperforation in the glass, the said microperforation having a depth of between 10 and 100 xcexcm, preferably between 15 and 60 xcexcm, particularly between 20 and 50 xcexcm, while xe2x80x9clow power of the laser beam or rayxe2x80x9d means a power at most sufficient to heat the glass without, or substantially without, perforating the glass (perforation of the glass to a depth of less than 10 xcexcm, preferably less than 2 xcexcm, particularly less than 1 xcexcm).
Advantageously, the focused pulsed laser forms, on the surface (preferably the external surface) of the glass, a series of impacts, defects or microperforations which are separated from each other, the said impacts, defects or microperforations having a depth in the glass of between 15 and 60 xcexcm, the distance separating two successive impacts, defects or perforations being advantageously greater than the depth of an impact, defect or perforation, but is preferably between 3 and 20 times the depth, particularly 4 to 10 times the depth of the defect, impact or microperforation.
Preferably, in the first step, during at least 3 rotations, preferably at least 5 rotations, particularly more than 10 rotations of the article to be cracked off, the region is subjected to the action of a continuous beam of laser rays or to continuous beams of laser rays so that the said beams touch the said region at one or more of the parts with a power density per unit area of less than 25 W/mm2, particularly between 5 W/mm2 and 20 W/mm2.
Advantageously, the pulsation of the laser beam or beams in the second step and/or the speed of rotation of the article to be cracked off are controlled so that two successive points of impact of the pulsed laser beam are separated from each other by a distance of less than 2 mm, preferably less than 1 mm, particularly by a distance of between 10 xcexcm and 1 mm, and more specifically by a distance of between 100 xcexcm and 800 xcexcm.
Advantageously, the pulsation of the laser beam is controlled so that the pulse frequency is between 500 and 1500 Hz, particularly between 800 and 1200 Hz.
According to one method of implementation, a region of from 2 to 8 mm in width is subjected, in the first step, to the action of one or more laser beams.
According to one advantageous method of implementation, between the first step and the second step, the region is not subjected to the action of a laser beam during a specific time period corresponding to at least 5% of the time period during which the region is subjected to the action of a laser beam or beams in the first step.
According to a preferred method of implementing the first step, the region is subjected to the action of one or more laser beams during at least a first and a second time period, these being separate from each other, while the region is not subjected to the action of a laser beam during an intermediate time period between the periods of treatment by means of one or more laser beams. Advantageously, the intermediate period corresponds to at least 5% of the first time period during which the region is subjected to the action of one or more laser beams in the first step.
According to one possible method of implementation, in the second step, separate parts of the region are simultaneously subjected to the action of a continuous beam of laser rays or continuous beams of laser rays and to the action of a focused pulsed laser beam respectively, so that each part of the region is touched by the continuous beam of laser rays or the continuous beams of laser rays before being touched by the focused pulsed laser beam. Advantageously, in the second step, separate parts of the region are simultaneously subjected to the action of a continuous beam of laser rays or continuous beams of laser rays and to the action of a focused pulsed laser beam respectively, so that each part of the region is touched by the continuous beam of laser rays or the continuous beams of laser rays for at least 0.05 seconds and preferably at least 0.1 seconds before being touched by the focused pulsed laser beam. Advantageously, each part of the region is touched by the continuous beam of laser rays or the continuous beams of laser rays, for no more than 1 second, preferably no more than 0.5 seconds, before being touched by the focused pulsed laser beam. In other words, the time period between the moment of impact of the continuous laser beam on a part of the region and the moment of impact of the pulsed laser beam on the said part of the region is preferably between 0.1 and 0.5 seconds.
In the method according to the invention, the focused pulsed beam of laser rays touches the region at points with a power density of more than 500 W, preferably more than 800 W, per point of impact. The power of the pulsed laser necessary for the method will depend on the thickness of the glass.
In the method according to the invention, the region is advantageously subjected to the action of a focused pulsed beam of laser rays and in that the pulse frequency of the laser beam is adjusted so as to form a series of points of impact in the region which is less than 500 xcexcm, advantageously less than 250 xcexcm, preferably less than 100 xcexcm, preferably less than 50 xcexcm, in diameter.
Advantageously, in the first step, a collimated laser beam is used, the power of which is, for example, less than 300 W.
The subject of the invention is also a continuous glassware crack-off plant for implementing the method according to the invention, the said plant comprising:
a device comprising a laser for carrying out the crack-off of a glass article forming a cracked-off rim for the article;
a device comprising a step-by-step drive system for bringing the glass articles successively towards the crack-off device; and
a drive system for rotating the glass articles about an axis at least during their crack-off operation. The plant according to the invention is characterized in that it includes two lasers, a first emitting a continuous beam of laser rays, while the second is a pulsed laser emitting a focused pulsed laser beam.
Advantageously, it includes at least one splitter for splitting the continuous beam of laser rays emanating from the first laser into at least a first and a second beam which are separate from each other and means for directing the said first and second separate beams respectively towards a first and second treatment region, so that an article to be cracked off is treated by the first beam in the first region, before being transferred by the step-by-step drive system to the second region where the article treated by the first beam is treated by the second beam. The splitter also makes it possible to be able to use a laser for the parallel treatment of several glass articles.
According to another embodiment, it includes at least one splitter for splitting the continuous beam of laser rays emanating from the first laser into at least a first and a second beam, which are separate from each other, and means for directing the said first and second separate beams respectively towards a first and second treatment region, so that an article to be cracked off is treated by the first beam in the first region, before being transferred by the step-by-step drive system to the second region where the article treated by the first beam is treated by the second beam before being treated by the focused pulsed beam of laser rays.
Preferably, the plant according to the invention includes means for adjusting the power of the pulsed laser, the pulse frequency of the pulsed laser ray and the speed of rotation of the glass articles to be cracked off.
In possible embodiments, the plant may include a cooling station and/or a station for flatting the cracked-off rim of the glass article and/or a station for fire-finishing the cracked-off rim of the glass article.
Finally, the subject of the invention is also a glass article having a cracked-off rim, the said rim being adjacent to a line consisting of points of impact of a laser ray which are separated from each other or correspond, at least partially, to a line consisting of points of impact of a laser ray which are separated from each other, the said points of impact having a diameter of less than 500 xcexcm, preferably less than 250 xcexcm, particularly less than 100 xcexcm, and more particularly less than 50 xcexcm, and being separated successively from each other by a distance of less than 2 mm, preferably less than 1 mm, particularly between 100 xcexcm and 800 xcexcm. Such an article may be easily flatted and may simply undergo fire-finishing without a prior flatting operation.